1. Field of the Invention
The present invention relates to a belt tension mechanism capable of providing tension to a photoconductive belt and a related image forming device, and more particularly, to a belt tension mechanism capable of releasing tension of a photoconductive belt when being not electrified and a related image forming device.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram of an image forming device 10 in the prior art. The image forming device 10 can be a printer, a multi-functional product, and so on. The image forming device 10 includes a housing 12 for covering inner components of the image forming device 10, a photoconductive belt 14, a charger 16, an exposing device 18, a developing device 20, a clean device 22, a transfer roller 24, a toner fuser 26, and a discharge unit 28.
When the image-forming device prints an image, as the first step of the entire process, a charger 16 charges a surface of a photoconductive belt 14 to a charged potential. The exposing device 18 exposes the photoconductive belt 14 to form a latent image on the photoconductive belt 14. The toners stored in the developing device 20 are jumped onto the latent image to form a toner image. The transfer roller 24 transfers the toner image on a print medium, such as paper. At last, the toner fuser 26 fuses the toners on the print medium 40. The clean device 22 cleans the rest toners on the photoconductive belt 14, and the discharge unit 28 discharges the rest charged potential on the photoconductive belt 14.
The image forming procedure of the image forming device 10 operates on the photoconductive belt 14 mostly. Thus the characteristic of the photoconductive belt 14 influences print quality directly. Generally, supporting components sustain the photoconductive belt to move along a path and define the outline of the photoconductive belt 14. Please refer to FIG. 2. FIG. 2 is a diagram of the photoconductive belt 14 in the prior art. A drive roller 44 and an idle roller 46 drive the photoconductive belt 14 so as to enlarge the size of the image forming device 10. Please refer to FIG. 1. U.S. Pat. No. 5,313,259 discloses the photoconductive belt 14 moving along a triangular path so that the size of the image forming device can be reduce. A tension roller 42 is for pressing the photoconductive belt 14 so as to provide tension to the photoconductive belt 14 and sustain the photoconductive belt 14. A drive roller 44 is for driving the photoconductive belt 14 to rotate. An idle roller 46 is for sustaining the photoconductive belt 14 with the tension roller 42 and the drive roller 44 together so that the drive roller 44 is capable of driving the photoconductive belt 14 smoothly. The tension roller 42 keeps pressing the photoconductive belt 14 causing the stress and the tension inside the photoconductive belt 14, especially for long idle period of the image forming device 10. It causes torsion and deformation of the photoconductive belt 14 and results in elasticity fatigue of the photoconductive belt 14 so that the service life of the photoconductive belt 14 and the print quality of the image forming device 10 reduce.
To solve the above-mentioned problem, different releasing mechanisms are designed for separating the tension roller and the photoconductive belt so as to release the tension of the photoconductive belt when the photoconductive belt does not operate. For example, U.S. patents of publication no. 20060120757, 20050002693, 20060024088 and U.S. Pat. Nos. 7,155,144, 7,024,136 disclose releasing mechanisms for releasing the photoconductive belt. However the conventional releasing mechanisms is only capable of separating the tension roller and the photoconductive belt when being electrified. It means that the tension roller and the photoconductive belt can not be separated by the conventional releasing mechanisms when the image forming device is not electrified or shut down abnormally so that the service life of the photoconductive belt and the print quality of the image forming device reduce.